With respect to the hardware design of IoT nodes, it may not be feasible to directly adopt the adaptive BF technology at IoT devices because it is difficult to equip expensive and bulky BF antennas at IoT nodes. However, appropriate configurations of IoT devices can extend the EH distance. For example, the sensitivity adjustment of the EH circuits can extend the powering distance [1]}. Another design consideration is the radio frequency. In previous studies, most of prototypes of WuRs/energy harvesters are based on the frequency about 2.4GHz, 400MHz, and 900MHz, where 2.4GHz-based circuits are more compatible for 802.11-based wireless communication networks, while 400MHz or 900MHz based circuits may result in longer communication range.
